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          <h1 class="post-title" itemprop="name headline">【教程学习】GLSL_Foundation</h1>
        

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        <blockquote>
<p>来源<a href="http://www.lighthouse3d.com/tutorials/glsl-tutorial/" target="_blank" rel="noopener">lighthouse3d</a>的GLSL教程<a id="more"></a></p>
</blockquote>
<p>在学习WebGL过程中，之前一直都是理解绘图的大致流程中的程序操作，这篇系统形象记录下整个流程。</p>
<p><img src="http://hi.csdn.net/attachment/201107/8/0_1310133375dwC8.gif" alt="流水线流程"></p>
<ul>
<li><p>Vertex Transformation（顶点变换)</p>
<p>这里一个顶点是一个信息集合，包括空间中的位置、顶点的颜色、法线、纹理坐标等。这一阶段的输入是独立的顶点信息，固定功能流水线在这一阶段通常进行如下工作：顶点位置变换、为每个顶点计算光照、纹理坐标的生成与变换。</p>
</li>
<li><p>Primitive Assembly and Rasterization（图元组合和光栅化)</p>
<p>此阶段的输入是变换后的顶点和连接信息（connectivity information）。连接信息告诉流水线顶点如何组成图元（三角形、四边形等）。此阶段还负责视景体（view frustum）裁剪和背面剔除。</p>
<p>光栅化决定了片断（fragment），以及图元的像素位置。这里的片断是指一块数据，用来更新帧缓存（frame buffer）中特定位置的一个像素。一个片断除了包含颜色，还有法线和纹理坐标等属性，这些信息用来计算新的像素颜色值。本阶段的输出包括：帧缓存中片断的位置、在顶点变换阶段计算出的信息对每个片断的插值。</p>
<p>这个阶段利用在顶点变换阶段算出的数据，结合连接信息计算出片断的数据。例如，每个顶点包含一个变换后的位置，当它们组成图元时，就可以用来计算图元的片断位置。另一个例子是使用颜色，如果多边形的每个顶点都有自己的颜色值，那么多边形内部片断的颜色值就是各个顶点颜色插值得到的。</p>
</li>
<li><p>Fragment Texturing and Coloring（片断纹理化和色彩化）</p>
<p>此阶段的输入是经过插值的片断信息。在前一阶段已经通过插值计算了纹理坐标和一个颜色值，这个颜色在本阶段可以用来和纹理元素进行组合。此外，这一阶段还可以进行雾化处理。通常最后的输出是片断的颜色值以及深度信息。</p>
</li>
<li><p>Raster Operations（光栅操作）</p>
<p>此阶段的输入：像素位置、片断深度和颜色值</p>
<p>在这个阶段对片断进行一系列的测试，包括：剪切测试（scissor test）、Alpha测试、模版测试、深度测试</p>
<p>如果测试成功，则根据当前的混合模式（blend mode）用片断信息来更新像素值。注意混合只能在此阶段进行，因为片断纹理化和颜色化阶段不能访问帧缓存。帧缓存只能在此阶段访问。</p>
</li>
</ul>
<p><img src="http://hi.csdn.net/attachment/201107/8/0_1310133462o5WH.gif" alt="更直观的流水线流程"></p>

      
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